USGS science for a changing world Streamflow in the Quinnipiac River Basin, Connecticut-Statistics and Trends, 1931-2000
Water-Resources Investigations Report 02-4217
Prepared in cooperation with the Connecticut Department of Environmental Protection
U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior U.S. Geological Survey
Streamflow in the Quinnipiac River Basin, Connecticut-Statistics and Trends, 1931-2000
By Elizabeth A. Ahearn
Water-Resources Investigations Report 02-4217
Prepared in cooperation with the Connecticut Department of Environmental Protection
East Hartford, Connecticut 2002 U.S. DEPARTMENT OF THE INTERIOR GALE A. NORTON, Secretary
U.S. GEOLOGICAL SURVEY Charles G. Groat, Director
The use of firm, trade, and brand names in this report is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey.
For additional information write to: Copies of this report can be purchased from:
District Chief U.S. Geological Survey U.S. Geological Survey Branch of Information Services 101 Pitkin Street Box 25286, Federal Center East Hartford, CT 06108 Denver, CO 80225 http://ct.water.usgs.gov CONTENTS
Abstract ...... 1 Introduction ...... 2 Purpose and scope ...... 2 Previous studies ...... 3 Description of basin...... 3 Acknowledgments ...... 3 Streamflow statistics ...... 3 Flow-duration statistics ...... 5 LO\V-flow frequency statistics ...... 5 Monthly mean and monthly median streamflow ...... 12 August median streamflow ...... 16 Streamflow trend analysis at the Wallingford gaging station ...... 17 Trend detection methods ...... 17 Trends in streamflow ...... 19 Factors that affect trends in streamflow ...... 23 Precipitation ...... 23 Wastewater discharges ...... 25 Summary ...... 29 References cited ...... 30 Appendix 1. Trend results of selected percentiles of streamflow between the annual minimum and annual maximum, Quinnipiac River at Wallingford, Conn., 1931-2000 ...... 33 Appendix 2. Trend results of annual and monthly precipitation data for selected stations in Connecticut, 1930-2000 ...... 39 Appendix 3. Trend results of wastewater-discharge data from municipal wastewater-treatment facilities in Meriden, Cheshire, and Southington, Conn. 1985-2001 ...... 41
FIGURES 1. Map showing location of the Quinnipiac River Basin, south-central Connecticut, and data-collection points ...... 4 Figures 2. to 19. Graphs showing: 2. Minimum, maximum, and period of record flow-duration curves (A), and monthly flow-duration curves (B) at Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000 ...... 8 3. Minimum, maximum, and period of record flow-duration curves (A), and monthly flow-duration curves (B) at Quinnipiac River at Southington, Conn. (01195490), 1988-2000 ...... 9 4. Low-flow frequency curves, Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000 (A) and Quinnipiac River at Southington, Conn. (01195490), 1988-2000 (B) ...... 11 5. Monthly median and monthly mean streamflow, Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000 (A) and Quinnipiac River at Southington, Conn. (01195490), 1988-2000 (B) ...... 13 6. Boxplots showing monthly streamflow, Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000 (A) and Quinnipiac River at Southington, Conn. (01195490), 1988-2000 (B) ...... 14
Contents ill FIGURES-Continued 7. Trends in annual August median streamflow, Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000 ...... 16 8. Annual maximum, mean, median, and minimum streamflow, Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000 ...... 18 9. Trends in annual minimum streamflow, Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000 ...... 21 10. Trends in annual maximum streamflow, Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000 ...... 22 11. Trends in annual median streamflow, Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000 ... 22 12. Annual total precipitation for five rain gages in and near the Quinnipiac River Basin, Conn., and LOWESS smooth line, 1930-2000 ...... 24 13. Annual minimum streamflow at two U.S. Geological Survey streamflow-gaging stations (Quinnipiac River at Wallingford, Conn.-01196500 and Quinnipiac River at Southington, Conn.-01195400), 1988-2000 ...... 26 14. Monthly total permitted wastewater discharges into the Quinnipiac River from the wastewater-treatment facility in Meriden, Conn., 1985-2001 ...... 26 15. Trends in wastewater discharges into the Quinnipiac River from the wastewater-treatment facility in Meriden, Conn., 1985-2001 ...... 28
TABLES 1. Annual and monthly flow duration, Quinnipiac River at Wallingford, Conn. (01196500), 1931-00 and Quinnipiac River at Southington, Conn. (01195490), 1988-2000 ...... 6 2. Annual lowest mean flows for indicated periods of consecutive days and indicated recurrence intervals, Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000 and Quinnipiac River at Southington, Conn. (01195490), 1988-2000 ...... 10 3. Monthly streamflow in percentiles, Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000 and Quinnipiac River at Southington, Conn. (01195490), 1988-2000 ...... 15 4. Monthly median streamflows for August and September, Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000 and Quinnipiac River at Southington, Conn. (01195490), 1988-2000 ...... 16 5. Trends for selected percentiles of streamflow between the annual minimum and annual maximum streamflows, Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000 ...... 19 6. Trends in wastewater discharge at selected wastewater-treatment facilities, Quinnipiac River Basin, Conn...... 27
CONVERSION FACTORS
Multiply By To obtain
inch (in.) 25.4 millimeter mile (mi) 1.609 kilometer square mile (mP) 2.590 square kilometer cubic foot per second (ft3/s) 0.02832 cubic meter per second million gallons per day (Mgal/d) 0.04381 cubic meter per second
iv Streamflow in the Quinnipiac River Basin, Connecticut-Statistics and Trends, 1931-2000 Streamflow in the Quinnipiac River Basin, Connecticut-Statistics and Trends, 1931-2000 by Elizabeth A. Ahearn
ABSTRACT the effects these factors have on streamflow trends. Changes in rainfall intensity and, to a lesser Streamflow statistics were updated for two extent, increases in residential and commercial U.S. Geological Survey continuous record stream development and expansion of storm drainage flow-gaging stations on the Quinnipiac River systems are probable causes for increases in the (01196500-Wallingford and 01195490-South annual maximum streamflow. No evidence was ington). The streamflow record from the Walling found to indicate that a precipitation trend is ford station was analyzed to determine trends in causing the increase in the annual minimum to streamflow quantity from October 1930 to annual median streamflow. Upward trends in September 2000. Trends were analyzed using the non-parametric Mann-Kendall test and magni wastewater discharge from municipal (Meriden, tudes estimated for selected percentiles of stream Cheshire and Southington) wastewater-treatment flow, ranging from the oth (annual minimum) to facilities were detected during 1985-01. Statistical lOOth (annual maximum) percentile. Trend tests evidence suggests that the wastewater-discharge were performed on various time periods (30-, 40-, trend increased at a rate consistent with the annual 50-, 55-, 60-, 65- to 70-year periods), all ending in minimum streamflow trend during 1985-01 and 2000, except for two periods (1931-1960 and that the increases in the annual minimum stream 1941-1971) that were studied as 30-year reference flow appear to be caused by increases in waste periods. water discharges. The two most prevalent trends were Flow regulation appears to have an effect on increases in the annual minimum and annual streamflow trends, particularly on base flows maximum streamflow during the period 1931-00. (annual minimum daily mean streamflow) from The annual minimum streamflow increased by an 1932 to 1939 when exceptionally low flows were average of 0.44 cubic feet per second per year recorded at a time of average to above-average (ft3/s/yr), and the annual maximum streamflow precipitation. Droughts during the early 1930's, increased by an average of 17 ft3/s/yr. Increasing early 1940's, and 1960's, and above-average streamflows were detected predominantly in the precipitation during the 1970's indicate that the lower half of the flow distribution (Oth to magnitude of the streamflow trends (annual 5oth ~ercentile) and in the annual maximum minimum to annual median) particularly for (lOOt percentile) streamflow for periods 1931- 1931-00 may, in part, be a result of the relation 00, 1941-00, and 1951-00. During 1961-00, the between precipitation variability and the time pattern changed-increasing streamflows were periods analyzed. The highest number of stream detected in the middle to upper half of the flow flow trends were detected during 1931-00, 1941- distribution (30th to lOath percentile). No trends 00 and 1961-00, coincident with the beginning of were detected during 1971-00. multi-year droughts. Flow regulation during the Trend analyses of precipitation (data from early period of record (1930's) appears to be the 1930 to 2000) and wastewater discharge (data predominant reason for the trend magnitude in the from 1985 to 2001) provide some evidence about annual minimum streamflow from 1931 to 2000.
Abstract INTRODUCTION icut DEP in 2000 to (1) compute current streamflow statistics from two continuous-record streamflow The Quinnipiac River is an important resource gaging stations (Wallingford 01196500 and South for economic development, industry, agriculture, water ington 0 1195490) that can be used for water-resource supply, and biological diversity in south-central planning, management, and regulatory activities; and Connecticut. Despite the river's abundant flow, water (2) analyze historical streamflow data for trends to demands periodically are greater than minimum streamflow. Water scarcity caused by an over-alloca document any long-term (30 years or greater) flow tion of the resource and (or) drought poses a challenge changes. Streamflow records from the two gaging to all water users. Three tributaries (Sodom Brook, stations in the Quinnipiac River Basin and results of segments of Misery Brook, and Harbor Brook) and the streamflow-trend analysis for the Wallingford gaging upper Quinnipiac main stem headwaters are listed in station provide data to improve the understanding of the Draft 2002 Connecticut Waterbodies Not Meeting past and current streamflow conditions in the basin. Water Quality Standards (Impaired Water List), pursuant to Sections 303(d) and 305(b) of the Federal Clean Water Act, prepared by the Connecticut Depart Purpose and Scope ment of Environmental Protection (DEP) for the U.S. This report presents streamflow statistics of Environmental Protection Agency (USEPA) (Connect duration, frequency, and quantity of annual, monthly, icut Department of Environmental Protection, written maximum, and minimum streamflow for two gaging commun., 2002). Flow alteration was a criterion used in designating these waterbodies as impaired. Low stations in the Quinnipiac River Basin. Streamflow streamflows call attention to the seriousness of limited statistics are presented in tabular and graphical form to supplies, and degradation of the resource has wide characterize the basin's water resources and estimate spread implications. Federal, State, and local agencies flows needed for water supply and allocation. The are concerned that declining streamflows are degrading report also presents trends in streamflow for 1931-00 the ecological health of the river. As demands for and at the Wallingford gaging station. Statistical techniques uses of water increase, consideration is directed to the used to perform the trend analysis and compute the effects of human influences on ecological health of the basin characteristics that affect streamflow processes river, and the balance between streamflow needed for are presented to provide perspective on the detected fish and wildlife habitat integrity and water use. The trends. In addition, the report briefly describes how and stream habitat and stream ecosystem are affected by to what extent climatic and human influences affect changes to the natural flow regime. streamflow characteristics. The natural flow of the Quinnipiac River has Streamflow records were retrieved from the been altered by numerous flow diversions resulting in USGS National Water Information System (NWIS) a complex, modified river system. This complexity is accessed on the World Wide Web at URL http://water evident during low-flow periods when diversions may data.usgs.gov/nwis. All analyses were based on histor cause some stream reaches to dry up, whereas other reaches may gain flow from treated wastewater ical average daily discharge records from two discharge. Flow-regulation patterns in the basin affect continuous-record streamflow-gaging stations oper the tributaries and main stem in different ways (Quin ated by the USGS on the main stem of the Quinnipiac nipiac River Watershed Partnership, 2000). Streamflow River. Records from the downstream station (Walling is decreasing (low flow) in the tributaries and in the ford-O 1196500) began in October 1930, and records headwaters where water primarily is withdrawn. A from the upstream station (Southington-01195400) large percentage of water that is diverted from the trib began in November 1987. In this report, all time 1 utaries eventually is returned as wastewater to the main periods are expressed in water years . stem of the Quinnipiac River, thereby increasing flows on the main stem. 1A water year is the 12-month period October 1 through Sep In response to the water allocation and stream tember 30 and is designated by the calendar year in which it ends; flow concerns in the basin, the U.S. Geological Survey thus, the year from October 1, 1930 through September 30, 1931 is (USGS) began a cooperative study with the Connect- called the 1931 water year.
2 Streamflow in the Quinniplac River Basin, Connecticut-Statistics and Trends, 1931-2000 Previous Studies combined maximum withdrawal capacity of 120.3 Mgal/d, and 19 wastewater discharges, with a Streamflow duration and frequency statistics combined maximum daily discharge of 44.6 Mgalfd were compiled in a water-resources inventory of the (Quinnipiac River Watershed Partnership, 2000). Quinnipiac River Basin by Mazzaferro and others ( 1979) for the Wallingford gaging station for the period 1931-60. In the early 1980's, Cervione (1982) and Acknowledgments Weiss (1983) summarized low- and high-flow frequency statistics for rivers in the State with appre Charles Fredette of the Connecticut DEP, and ciable record length. Low- and high-flow frequency Glenn A. Hodgkins and Phillip J. Zarriello of the statistics for the Quinnipiac River at Wallingford USGS provided valuable technical insight and review gaging station are included in these two studies. The of the report. Barbara Korzendorfer, USGS, provided later studies benefited from longer records and super assistance in editorial review and report production. sede the statistics in the earlier report by Mazzaferro and others. Monthly, annual, and period of record streamflow statistics and a limited number of duration STREAMFLOW STATISTICS statistics are published annually by the USGS in the Statistical analysis of hydrologic data is impor Water-Resources Data series. tant in understanding streamflow variability, estimating future water supplies, and establishing new policies Description of Basin and regulations for managing water resources. Some of the most commonly used streamflow statistics include The Quinnipiac River Basin is in south-central flow duration, flow frequency (recurrence of a given Connecticut and drains an area of about 166 mi2 flow), averages, and percentiles of daily flows. Flow (fig. 1). The Quinnipiac River originates in the town of duration characterizes past streamflow by ranking the New Britain and flows southward for approximately distribution of flows over the analyzed period of 38 mi through the towns of Plainville, Southington, record. Flow-frequency estimates the probability of a Cheshire, Meriden, Wallingford, North Haven, and given streamflow occurring in the future. Averages and New Haven to Long Island Sound. The lower 9 mi of percentiles describe the central tendency and distribu the Quinnipiac River are affected by tides from Long tion of streamflow data. Island Sound. Major tributaries are the Eightmile The Wallingford gaging station (0 1196500~ River, Tenmile River, Misery Brook, Broad Brook, 3 Harbor Brook, Sodom Brook, Wharton Brook, and fig. 1) had a mean annual flow of217 ft /s Muddy River. Subregional basins of the major tribu (140 Mgalld), a historical minimum daily mean flow of 2 3 taries range from 5 to 22 mi . Land use is predomi 9.0 ft /s (5.8 Mgalld) recorded on November 2, 1930, nantly forest, agriculture, and residential in the upper and a historical maximum daily mean flow of 3 basin and predominantly densely developed urban and 7,210 ft 1s (4,660 Mgalld) recorded on June 6, 1982. industrial in the lower basin. The monthly median streamflow ranged from a low of 79.2 ft31s (51.2 Mgalld) in August to a high of294 ft3/s The USGS operates two continuous-record (190 Mgalld) in March. streamflow-gaging stations on the Quinnipiac River-at Wallingford (station 01196500) and at The Southington gaging station (01195490; Southington (station 01195490). The Wallingford fig. 1) had a mean annual flow of 34.2 ft3Is station was established in October 1930 and has a (22.1 Mgalld), a historical minimum daily mean flow 2 drainage area of 115 mi , which is approximately of 3.8 ft31s (2.5 Mgalld) recorded on August 20, 1999, 70 percent of the basin. The Southington station was and a historical maximum daily mean flow of 810 ft31s established in November 1987 and has a drainage area (523 Mgalld) recorded on October 21, 1999. The 2 of 17.4 mi , which is 10 percent of the basin. monthly median streamflow ranged from a low of An assessment of water diversions in 2000 iden 11.7 ft31s (7.56 Mgalld) in September to a high of tified 103 consumptive water withdrawals, with a 38.4 ft3 Is (24.8 Mgalld) in April.
Streamflow Statistics 3 73"0' 72"48'
Inset shows location of Ouinnipiac River Basin 41"36'
EXPLANATION
'\.. · · .r Basin ·\ boundary
01196500 Streamflow- .& gaging station ana number
650n.o.. National Oceanic .,.... and Atmospheric Administration rain gage and number
0 2 4 MILES I I 41 "24' I I 0 2 4 KILOMETERS
I$ ' \ \ \ \ \ (
Base from U.S. Geological Survey di gital line graph (1988)
Figure 1. Location of the Quinnipiac River Basin, south-central Connecticut, and data-collection points.
4 Streamflow in the Quinnipiac River Basin, Connecticut-Statistics and Trends, 1931-2000 Flow-Duration Statistics ingford gaging station, water year 1966 was the driest water year because of the extent and severity of the low Annual and monthly flow-duration statistics flows. The minimum daily mean streamflow in water were calculated for the Wallingford and Southington year 1966 at the Wallingford gaging station was gaging stations (table 1; figs. 2 and 3). Flow-duration 14.0 ft3/s. statistics represent the percentage of time specified streamflows were equaled or exceeded over the anal Because of the relatively short record of the ysis period. For example, the daily flows at the Wall Southington gaging station (12 years), compared to the ingford gaging station were greater than or equal to Wallingford station, the minimum and maximum flow 85.9 ft3/s 50 percent of the time (table 1) in October durations for each duration grouping in the period of during the period 1931-00. Because flow-durations record (1988-00) are used to emphasize the variation in statistics are performed on the rank position of a flow durations (fig. 3A). At the minimum limit, streamflow 3 value, the chronology of the flows is concealed. No was equal to or greater than 15 ft /s (9.7 Mgalld) indication is given of the date on which the flows 50 percent of the time in a single year (water year occurred. Flow-duration statistics are estimated by 1999). At the maximum limit, streamflow was equal to 3 arranging (by month) all the daily mean streamflows or greater than 33 ft /s (21 Mgalld) 50 percent of the for the given time period in ascending order without time in a single year (water year 1990). From the 12- regard to the sequence of the occurrence. The data then year average (1988-00) at the Southington gaging are grouped into class intervals by ascending order and station, streamflow was equal to or greater than 3 the probabilities of specified streamflow being equaled 25.1 ft /s (16.2 Mgalld) 50 percent of the time. or exceeded are computed. Flow-duration statistics Generally, flow-duration statistics apply to the were estimated by using the DVSTAT Computation period of record for which the data were analyzed. computer program in the USGS National Water Infor Where the period of record used to compute the statis mation System following USGS standard methods for tics is sufficiently long, flow-duration statistics can be estimating flow duration (Searcy, 1959) at gaging used as an indicator of probable future flows (Searcy, stations. The duration analysis provides values for 1959); however, if diversions, return flows, or climatic exceedance percentages based on the class limits and factors affecting flow are expected to change substan the percentage of all days in which a class limit was tially, flow-duration statistics cannot be used to indi equaled or exceeded. cate probable future flows with statistical certainty. For the Wallingford gaging station, the wettest and driest water years on record (fig. 2A) show a wide Low-Flow Frequency Statistics range in the percentage of time specified streamflows were equaled or exceeded in a single year. During the Frequency analysis can be used to obtain the wettest year on record (water year 1984), streamflow probability that specific streamflow will be equaled or was equal to or greater than 259 ft3/s (167 Mgalld) exceeded. The major application of low-flow 50 percent of the time; during the driest year (water frequency analysis is for setting flow standards associ year 1966), streamflow was equal to or greater than ated with diversion permits and for prediction purposes 56.3 ft3/s (36.4 Mgal/d) 50 percent of the time. From in water-resources planning. Two commonly used the long-term average (1931-00) at the Wallingford indices of low flow are the 7-day, 10-year low flow, gagin~ station, streamflow was equal to or greater than (7Q10), the lowest streamflow for a period of7 consec 152ft /s (98.2 Mgal/d) 50 percent of the time. utive days that is expected to occur once in a 10-year The driest and wettest years are defined as water period, and the 30-day, 2-year low flow, (30Q2), the years with the overall greatest number of minimum and lowest streamflow for a period of 30 consecutive days maximum flow durations in a water year. During water that is expected to occur once every other year. The year 1966 (driest water year), the 10- to 90-percent most widely used low-flow frequency statistic in flow duration ranged from 26 to 168 ft3Is and were the Connecticut is the 7Q10 flow, which is used by many lowest flows for that duration range in 70 years. During State and local agencies and by the USEPA to regulate water year 1984 (wettest water year), the 20- to SO wastewater discharges to streams. The Connecticut percent flow duration ranged from 138 to 473 ft3/s and DEP adopted as State policy the 7Q 10 statistic as a were the highest flows for that duration range in minimum flow event for which water-quality standards 70 years. Although water year 1931 had the lowest are expected to be met (Connecticut Department of daily mean streamflow (9.0 ft3/s) recorded at the Wall- Environmental Protection, 1997).
Streamflow Statistics 5 m Table 1. Annual and monthly flow duration, Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000 and Quinnipiac River at Southington, Conn. (01195490), 1988-2000
Duration Streamflow, In cubic feet per second (in Novem Decem Septem October January February March April May June July August Annual percent) ber ber ber U.S. Geological Survey station 01196500, Quinnipiac River at Wallingford 99 22.7 30.8 42.9 50.0 62.3 105 97.4 71.8 53.0 30.1 19.6 25.6 34.7 98 35.3 39.7 49.8 61.6 70.8 115 107 82.2 57.0 36.1 26.8 33.7 40.7 97 39.7 43.8 55.7 67.1 82.0 123 115 87.3 61.0 40.6 33.2 35.5 44.1 96 41.0 47.1 60.6 71.9 89.5 130 123 92.3 63.7 43.2 35.3 37.2 47.5 95 42.4 50.3 64.7 76.2 92.5 137 129 95.6 66.3 45.6 37.4 38.9 50.0 90 48.3 63.3 76.5 91.3 107 164 152 Ill 75.9 53.9 44.1 44.3 60.9 85 52.4 71.9 87.6 104 119 186 169 124 83.5 59.4 50.3 48.5 70.3 80 56.6 78.0 99.2 116 130 203 184 135 90.2 64.2 55.3 52.1 79.4 75 60.7 84.0 110 126 144 218 200 148 96.3 68.5 59.4 55.8 88.7 70 64.8 92.2 122 136 157 233 215 161 102 72.9 63.4 59.4 98.4 65 69.5 101 133 146 170 246 230 172 108 77.4 67.2 63.0 110 I 60 74.3 111 147 156 184 260 245 184 114 81.9 71.1 67.3 122 55 79.6 122 160 170 199 276 261 196 121 87.5 75.2 71.8 136 50 85.9 134 173 184 215 295 280 207 129 93.1 79.5 76.4 152 45 92.3 148 187 199 234 317 299 220 138 98.6 83.9 81.6 169 40 100 163 202 215 253 342 321 233 147 104 89.7 86.9 188 35 109 180 222 232 272 370 346 250 159 111 96.1 93.3 208 30 121 199 245 257 295 400 373 268 173 120 104 101 232 25 137 222 273 288 322 439 411 292 192 132 113 110 258 20 164 250 307 331 358 488 455 322 215 147 130 124 297 15 200 297 355 384 408 551 520 358 251 166 152 145 347 10 249 368 439 487 482 661 628 413 311 195 190 184 424 5 360 533 601 724 643 969 842 521 431 266 260 277 587 2 576 760 888 1,140 957 1,320 1,240 702 694 410 408 510 904 843 896 1,220 1,460 1,270 1,730 1,530 962 1,070 535 637 822 1,210
----·····------Table 1. Annual and monthly flow duration, Ouinnipiac River at Wallingford, Conn. (01196500), 1931-2000 and Ouinnipiac River at Southington, Conn. (01195490), 1988-2000-Continued
Duration Streamflow, in cubic feet per second (in Novem Decem Septem October January February March April May June July August Annual percent) ber ber ber U.S. Geological Survey station 01195490, Quinnipiac River at Southington 99 5.30 8.70 8.00 11.2 12.9 15.6 16.8 13.6 7.30 5.00 4.00 4.10 4.80 98 5.50 .9.00 8.30 11.6 13.8 16.2 18.2 14.4 7.90 5.20 4.10 4.30 5.50 97 5.70 9.20 8.70 12.0 15.3 16.9 19.3 15.1 8.40 5.60 4.30 4.50 6.20 96 6.00 9.40 9.10 12.4 16.2 17.7 20.2 15.5 8.70 5.90 4.50 4.90 6.80 95 6.36 9.62 9.60 12.8 17.1 19.4 20.7 15.9 9.06 6.16 4.63 5.15 7.35 90 7.22 11.4 13.5 14.7 19.2 25.2 22.7 18.1 10.8 7.34 5.34 6.25 9.42 85 7.76 12.5 15.5 16.5 20.8 27.5 24.2 19.3 12.3 8.15 6.52 7.12 11.6 80 8.50 13.4 17.4 18.2 22.7 29.0 25.9 20.7 13.1 8.85 7.81 7.80 13.3 75 9.50 14.7 19.0 19.8 24.1 30.5 27.8 22.4 13.9 9.75 8.77 8.51 15.0 70 11.1 17.2 20.4 21.5 25.5 31.9 29.7 24.2 14.6 11.1 9.75 9.12 16.8 65 12.5 19.8 21.5 23.9 26.8 33.4 31.6 25.8 15.6 12.1 10.9 9.61 18.8 60 13.7 21.3 22.7 25.9 28.4 34.8 33.5 27.6 16.7 13.0 11.8 10.2 20.8 55 14.8 23.2 24.0 27.7 30.2 36.1 35.9 29.5 17.9 13.9 12.6 11.0 22.9 50 15.8 24.9 25.3 29.2 32.1 37.5 38.4 31.4 19.2 14.9 13.4 11.7 25.1 45 17.6 26.8 26.7 31.0 34.2 39.0 40.8 33.2 20.6 16.0 14.2 12.5 27.4 40 19.4 29.1 28.5 33.1 36.2 40.8 43.2 35.3 22.3 17.1 15.1 13.5 29.8 35 21.3 31.7 30.8 35.4 38.2 42.9 46.1 37.6 24.4 18.3 16.0 15.0 32.7 30 24.1 35.6 33.6 37.9 40.6 46.1 49.2 41.0 26.6 20.1 17.7 16.4 35.7 25 27.3 40.5 37.3 41.8 44.5 51.5 52.7 45.8 29.3 22.5 19.7 18.2 39.5 20 32.5 44.8 42.7 47.3 48.3 58.6 58.5 52.1 33.5 24.9 23.3 21.2 44.6 15 39.0 51.6 50.3 56.6 55.3 71.5 63.4 61.4 40.5 29.1 28.4 24.7 52.2 10 48.3 66.2 63.4 69.1 63.5 92.2 73.3 74.6 50.5 36.4 37.6 31.5 64.6 5 81.5 97.2 90.2 106 85.7 151 98.0 102 74.7 66.4 64.7 49.5 91.8 2 179 136 121 193 104 184 133 187 95.2 98.7 140 106 154 276 172 153 223 125 199 250 258 186 144 234 166 200 A. 1o. ooo rr------,---,----r---.--r---.------,,..--~~ WA LLINGFORD
0z 0 (,) liJ Ul a: liJ c.. 1- 1,000 liJ liJ u. (,) iii :::> (,) ~ ~ 0 ...J u. :E 100 10 -~~------~-...J_ ___ ...J__~_...J_ _ _L___ ~--~~ 0.9 1.0 10.0 20 .0 50.0 70.0 80.0 90.0 98.0 99.0 99.2 PERCENTAGE OF TIME STREAMFLOW EQUALED OR EXCEEDED B. 2,000 WALLINGFORD 1,000 0z 0 (,) liJ Ul a: liJ c.. 1- liJ liJ u. (,) iii :::> (,) 100 ~ ~ 0 ...J u. :E 1 0L-L-----~-~-~~_L~_L__~_~ _ _L_ _L__ L_ _ _L~ 0.9 1.0 5.0 10.0 20.0 30 040.050.0 70.0 80.0 90.0 95.0 98.0 99.0 99.2 PERCENTAGE OF TIME STREAMFLOW EQUALED OR EXCEEDED Figure 2. Minimum, maximum , and period of record flow -duration curves (A), and monthly flow-duration curves (B) at Ou inn ipiac River at Wallingford, Conn. (01196500), 1931 - 2000. 8 Streamflow In the Quinniplac River Basin, Connecticut-Statistics and Trends, 1931-2000 A. 1.000 SOUTHINGTON 0 z 0 () w (/) cr w c.. 100 1- w w u.. () iii ::> () ~ ~- 0 ..J 10 u.. ::!: 1 0.9 1.0 5.0 10.0 20.0 50.0 70.0 80.0 90.0 99.0 99.2 B. PERCENTAGE OF TIME STREAMFLOW EQUALED OR EXCEEDED 300 SOUTHINGTON OCT NOV DEC JAN FEB MA R 0 APR z 100 - MA Y 0 JUNE () w JULV - AUG (/) cr SEPl w c.. 1- w w u.. () iii ::> () ~ ~ 0 ..J u.. 10 ::!: 3 0.9 1.0 2.0 5.0 10.0 20.0 30.040.050.060.070.0 80.0 90.0 98.0 99.0 99.2 PERCENTAGE OF TIME STREAMFLOW EQUALED OR EXCEEDED Figure 3. Minimum, maximum, and period of record flow-duration curves (A), and monthly flow-duration curves (B) at Ouinnipiac River at Southington, Conn . (01195490), 1988-2000. Streamflow Statistics 9 The 7QIO computed for the period of record interval is the average length of time, usually stated in (1931-00 Wallingford; 1988-00 Southington) is years, between the exceedance of particular streamflow 33.4 fr31s (21.6 Mgalld) for the Wallingford gaging magnitudes. Low-flow frequency statistics are station and 4.32 ff Is (2.79 MgaUd) for the Southington computed from a series of annual minimum flows and gaging station (table 2; fig. 4). The 30Q2 computed for can be computed for any combination of days of the period of record is 61.8 ft3/s (39.9 Mgalld) for the minimum flows. Wallingford gaging station and 9.01 ft31s (5.82 MgaUd) for the Southington gaging station (table 2; fig. 4). Low-flow frequency statistics for Wallingford Stated in terms of probability (1 divided by the recur and Southington gaging stations (table 2; fig. 4) were rence interval), the 7-day annual minimum streamflow calculated with the USGS computer program SWSTAT at the Wallingford gaging station has a 10-percent (Lumb and others, U.S. Geological Survey, written 3 chance in any year of being less than 33.4 ft 1s (21.6 colllinun., 1994) for minimum 1-day flows and the Mgal/d); the 30-day annual minimum streamflow at the minimum average daily flow for n-days, where n Wallingford gaging station has a 2-percent chance in equals 2, 3, 7, 10, 30, 60, 90, 120, 183, and 365 consec any year of being less than 61.8 ft3Is (39 .9 Mgal/d). utive days for each year of record. Then-day low flows Frequency statistics relate magnitude of a given were fitted to a log-Pearson Type III distribution curve streamflow to recurrence interval. The recurrence to calculate recurrence frequencies. Table 2. Annual lowest mean flows for indicated periods of consecutive days and indicated recurrence intervals, Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000 and Quinnipiac River at Southington, Conn. (01195490), 1988-2000 [--, low-flow frequency estimates beyond a 20-year recurrence interval are considered unreliable and were not calculated] Period of Annual lowest mean flows (in cubic feet per second) for indicated recurrence Intervals (in years) consecu- tlve days 1.25 2 5 10 20 50 100 U.S. Geological Survey station 01196500, Quinnipiac River at Wallingford, April1, 1932 to March 31,2000 1 56.6 40.6 26.2 20.0 15.6 11.5 9.2 2 58.5 42.9 28.7 22.4 17.8 13.5 11.0 3 59.4 45.8 32.5 26.2 21.6 16.9 14.2 7 64.9 51.5 39.2 33.4 29.0 24.5 21.8 10 67.4 52.5 40.2 34.8 30.7 26.7 24.2 30 81.2 61.8 48.1 42.6 38.6 34.8 32.6 60 96.9 72.7 55.7 48.9 44.1 39.4 36.7 90 108 80.5 61.7 54.2 49.1 44.1 41.2 183 155 112 83.8 72.6 64.9 57.5 53.2 365 264 212 167 147 131 114 104 U.S. Geological Survey station 01195490, Quinnipiac River at Southington, April!, 1989 to March 31, 2000 1 8.64 6.36 4.72 4.06 3.59 2 8.77 6.41 4.76 4.09 3.63 3 8.90 6.47 4.81 4.15 3.69 7 9.43 6.83 5.03 4.32 3.82 10 9.98 7.14 5.18 4.41 3.87 30 13.28 9.01 6.26 5.23 4.52 60 16.1 11.2 7.89 6.61 5.73 90 20.0 13.9 9.76 8.19 7.10 183 27.6 19.9 15.3 13.7 12.6 365 39.9 32.8 26.7 24.0 21.9 10 Streamflow In the Quinnipiac River Basin, Connecticut-Statistics and Trends, 1931-2000 A. 1.000 c (/) >- WALLINGFORD z <( 0 500 0 (.) l!J w > en >= ::J a: u w l!J (/) 0.. z 1- 0 w u w u. 365 u. 100 0 (.) 0 0 iii a: 183 :::> 50 l!J (.) 0.. 90 ~ tO ~ 0 ...J u. :E c:x: 10 - w a: EX AMPL E: The 7-day annual low flow will be 1- en 5 less than or equal to 33.4 cubic feet per second z (2 1.6 million gallons per day) at intervals averaging 10 years. c:x: w :E 1-en w 3: 0 ...J 1.25 2 5 10 20 50 100 R E CURRENCEINTERVA ~I NYEARS B. c 100 z 0 SOU TH INGTON (.) w en (/) a: >- w <( 0.. 0 l!J 1- > w >= w ::J u.. u 365 l!J (.) (/) z iii 0 :::> u (.) u. 183 0 ~ 0 ~ 10 0a: 0 l!J ...J 0.. 90 u. :E 60 c:x: w 30 a: 1- m z c:x: w :E EXAMPLE: The 7-day annual low flow will be 1- less than or equal to 4.32 cubtc feet per second m w (2 .79 million gallons per day) at intervals averaging 10 years . 3: 0 ...J 1.25 2 5 10 20 RECURRENCE INTERVAL, IN YEARS Figure 4. Low·flow frequency curves, Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000 (A) and Quinn ipiac River at Southington, Conn. (01195490), 1988-2000 (8 ). Streamflow Statistics 11 The reliability of low-flow frequency statistics is for the years 1988-00. Mean streamflow shows a related closely to the length of record used to compute maximum in March at the Wallingford gaging station the frequency statistics. At least 10 years of record are of383 ft3/s (247 Mgalld) and at the Southington gaging needed to determine the statistics (7Q10) with reason station of 50.1 ft3/s (32.4 Mgalld) in response to precip able confidence (Ries, 2000). The results from the low itation, snowmelt, and soil-moisture content. frequency analysis can be used as an indication of Increasing evaporation and transpiration during the probability that certain flow events will occur in the growing season contribute to a minimum mean flow at future, assuming the human influences on streamflow the Wallingford gaging station of 110 ft3/s are expected to remain unchanged. The low-flow (71.1 Mgal/d) in August and at the Southington gaging frequency statistics for both the Wallingford and South station of 1g.1 ft 3/s (12.3 Mgal!d) in September. Mean ington gaging stations should not be used to predict streamflow generally is much larger than the median future flows because of the changing flow regulation streamflow because very large streamflow values often during the period of record affecting natural stream associated with storm events affect the mean appre flow. The frequency statistics presented in table 2 ciably more than the median. reflect the overall period of record that includes past Boxplots (figs. 6A and 6B) illustrate the central flow regulation at the Wallingford and Southington tendency and variability in monthly streamflow, and gaging stations. Because the Southington gaging provide a graphical representation of distribution and station has a relatively short record (12 years), range of the data. The top and bottom of the box repre compared to the Wallingford gaging station, the sent the 75th and 25th percentiles, respectively, and maximum low-flow frequency estimated at the South bracket the central 50 percent of the flow data for a ington gaging station is 20 years. Low-flow frequency given month. The centerline splitting the box repre estimates beyond a 20-year recurrence interval at the sents the median (50th percentile) and is defined as the Southington gaging station are considered unreliable median of all the daily discharges during the period of and, therefore, were not calculated. record for that month. The lines drawn from the ends of When streamflows are altered by diversions, the box extend to the 1oth and 9oth percentiles of the reservoirs, and wastewater discharges, the natural data. Streamflows that are less than the 10th and greater 7Q I 0 flow cannot be estimated from a frequency anal than the goth percentiles d.efine and emphasize the ysis of streamflow data. For rivers that are altered extreme values. The largest 10 percent (for example, largely by regulation, the 7Ql0 low flow can be major flood events) and smallest 10 percent (for computed from a regional regression equation. Low example, droughts) of the streamflow data values are streamflows (such as the 7Ql0) are highly dependent not shown. on the geologic characteristics of the basin (Thomas, From the boxplots (figs. 6A and 6B), it can be 1966). The regression equation developed by Cervione seen that August and September have similar flow (1982) for estimating the 7Ql0 in Connecticut is based characteristics at each station, as indicated by almost on the percentage of the basin underlain by coarse identical percentiles used to define the boxplots. From grained deposits. The 7Ql0 computed from the regres 3 25 to 7 5 percent of the observed streamflows in August sion equation is 30.2 ft /s (19.5 Mgal/d) for the Wall and September range from about 60 to 110 ft3/s (3g to 3 ingford gaging station and 6.21 ft /s (4.01 Mgal!d) for 71 Mgalld) at the Wallingford gaging station, and from the Southington gaging station. The estimated 7Q10 about g.o to 18 ft3/s (5.8 to 12 Mgalld) at the South value for Wallingford from the regression equation is ington gaging station. 10 percent less than the 7Q10 calculated from the station data. The estimated 7Q10 value for Southington Monthly streamflow percentiles used to create from the regression equation is 30 percent greater than the boxplots (10-, 25-, 50-, 75-, 90-percentiles) and the 7Q 10 calculated from the station data. monthly minimum, maximum, and mean streamflows are listed in table 3. The 10th percentile indicates that Monthly Mean and Monthly Median 90 percent of the streamflow equals or exceeds this Streamflow value for a given month. Conversely, the goth percentile indicates that 10 percent of the streamflow equals or Monthly mean and monthly median streamflow exceeds this value for a given month. These descriptive (figs. SA and 5B) were calculated from the daily mean statistics summarize information about the distribution streamflow for the Wallingford gaging station for the of streamflow in a given month for the period of record. years 1931-00 and for the Southington gaging station The percentiles are reciprocals of flow durations. 12 Streamflow in the Qulnnipiac River Basin, Connecticut-Statistics and Trends, 1931-2000 A. 450 c WALLINGFORD > z < 400 c 0 a: 0 - 250 w w a. en - c rronthty rood ian a: 350 en w z a. o rronthly rrean 0 200 _J t- 300 _J w < w (!J u. ,...... - 250 z 0 - 0 m - 150 :J :::;) _J 0 200 ....- ~ ~ ....- ~ ~ 150 100 0 ~ _J r- 0 u. r- _J r-- u. ~ 100 - ~ ,•( __.__ 0 _ 0 JAN F83 fv\1\R AFR MA.Y JUN JUL AUG SEP OCT NOV DEC '------ B. SOUTHINGTON 60 c > z c< 0 35 a: 0 w w 50 - a. en en a: ....- 30 z w [!] rronthly rredian 0 a. ....- _J _J 40 r- o rronthly rrean 25 tij r- < w (!) u. z 0 - - 20 0 m 30 :J ;:) - - _J 0 15 :E ~ - 20 r-- ~ ~ .. - 0 10 ~ _J 0 u. _J I u. ~ 10 . ~ < ~ 5 w '------Figure 5. Monthly median and monthly mean streamflow, Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000 (A), and Quinnipiac River at Southington, Conn. (01195490), 1988-2000 (B). Streamflow Statistics 13 A. 0 WALLINGFORD z 8 600 UJ (/) a: UJ a. 500 1- UJ UJ u. ~ 400 al :::> (.) ~ 300 i 0 _J u. 200 :E ~ a:UJ t;; 100 0 JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC EXPLANATION 90th percentile 75th percentile Median B. 25th percentile ~ 1Oth percentile 0 SOUTHINGTON z 90 0 (.) UJ (/) 80 a: UJ a. 70 1- UJ UJ u. 60 ~ m :::> 50 (.) z 40 i 0 _J 30 u. :E ~ 20 a:UJ 1- (j) 10 0 JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC Figure 6. Monthly streamflow, Quinnipiac River at Wallingford, Conn. (011 96500). 1931-2000 (A) and Quinnipiac River at Southington, Conn. (01195490), 1988-2000 (B) 14 Streamflow in the Quinnipiac River Basin, Connecticut-Statistics and Trends, 1931-2000 Table 3. Monthly streamflow in percentiles, Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000 and Ouinnipiac River at Southington, Conn. (01195490), 1988-2000 (Percentiles were determined from daily mean flows using SPLUS software] Maximum 50th- 90th- 75th- 25th- lOth- Minimum Daily Month (daily percentile percentile percentile percentile percentile (daily mean) mean mean) (median) U.S. Geological Survey station 01196500, Quinnipiac River at Wallingford, water years 1931-2000 January 4,100 480 285 183 126 91 37 261 February 3,290 481 322 215 142 105 36 273 March 2,800 651 438 295 218 164 80 383 April 3.360 630 410 277 199 152 80 358 May 3,300 411 294 207 149 110 27 248 June 7,210 306 193 128 96 76 40 185 July 1,610 193 131 92 68 53 16 118 August 3,160 190 112 79 60 43 13 110 September 3,770 180 109 76 55 44 12 114 October 3,350 250 136 85 61 48 10 134 November 2,080 361 220 134 83.8 63 9 188 December 2,620 437 270 172 110 76 17 230 U.S. Geological Survey station 01195490, Quinnipiac River at Southington, water years 1988-2000 January 374 67.8 41 28 19 14 7.7 39.4 February 251 62.3 44 31 24 19 12 37.9 March 348 90 51 37 30 24.2 15 50.1 April 360 72.1 52 38 27 22 15 45.9 May 313 73.8 45 31 22 18 12 42.1 June 724 51 29 19 13 10 6.5 28.4 July 230 36.6 22 14 9.6 7.4 4.7 20.9 August 283 35.8 19 13 8.9 5.3 3.8 21.8 September 704 30.1 18 11 8.5 6.3 3.9 19.1 October 810 47.9 27 15 9.5 7.1 5.1 28.9 November 289 62 37.3 24 14 11 7.9 33.3 December 227 61.6 37 25 18.5 13 7.7 33.2 Streamflow Statistics 15 August Median Streamflow The computed August median flow (table 4) may not be the appropriate flow for maintaining aquatic The August median flow, also called the aquatic habitat as recommended by the USFWS because of the base flow (ABF), is a streamflow statistic used by many extent of regulation affecting streamflows. The USFWS Federal and State regulators as the minimum streamflow states that the ABF should be determined from unregu required for maintaining aquatic habitat in New England lated streamflow. The September median flow is shown streams. The U.S. Fish and \Vildlife Service (USFWS) to illustrate the similarity of the monthly averages during recommends computing the aquatic base flow as the late summer when low-flow conditions are present. median of all the August monthly means (U.S. Fish and September flows are less than August flows. Wildlife Service, 1981). Alternatively, Charles Ritzi and Associates (1987) computed the ABF as the median of Table 4. Monthly median streamflows for August and the August daily mean flow. From a time-series plot September, Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000 and Quinnipiac River at Southington, (fig. 7) of August median flows from 1931 to 2000 at the Conn. (01195490), 1988-2000 Wallingford gaging station, it can be seen that the [All values in cubic feet per second. USFWS, U.S. Fish and Wildlife Service] medians differ considerably from year to year. The Sep- 3 U.S. Geological Computed August August median flow ranged from a low of 25 ft /s tember Survey station from median ( 16 Mgal/d) in water year 1966 to a high of 218 ft3/s median (141 Mgalld) in water year 1938. The extremes in 1966 Quinnipiac River at Daily means 79.0 76.0 and 1938 August median streamflows reflect the end of Wallingford Monthly 90.1 89.1 (01196500) multi-year drought period and a hurricane, respectively. means (USFWS) The LOWESS smooth curve illustrates the general trends in the August median flow that have taken place Quinnipiac River at Daily means 13.0 11.0 since 1931. The smooth line shows the August median Southington Monthly 20.7 12.4 now dipped to the lowest point in 70 years during the (01195490) means multi-year drought in the 1960's. (USFWS) 250 I I I I I I I I Cl z LOWESS smooth -- 0 () w (/) a: w 200 t- a. ...w w LL () iii ::::> () 150 r- - ~ ~ 0 ..J LL z I I 0 1930 1940 1950 1960 ~ 1970 1980 1990 2000 WATER YEAR Figure 7. Trends in annual August median streamflow, Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000. 16 Streamflow in the Quinnipiac River Basin, Connecticut-Statistics and Trends, 1931-2000 STREAMFLOW TREND ANALYSIS AT THE 30-yearperiods (1931-1960 and 1941-1970) that were WALLINGFORD GAGING STATION studied as reference periods. A time-series plot of the annual minimum and Statistical procedures were used to detect trends maximum streamflow bracketing the annual mean and in the streamflow data and to evaluate how streamflow median flows was used to make preliminary inferences has changed over the entire streamflow range (annual concerning streamflow over time (fig. 8). Statewide, minimum to annual maximum). Long-term streamflow multi-year droughts occurred from July 1929 to records at the Wallingford streamflow-gaging station December 1932, from September 1940 to April1945, were examined for trends during the period 1931-00. and from August 1961 to November 1971 (Weiss, Streamflow records at the Southington streamflow 1991). Scatterplots of streamflow percentiles were gaging station were not examined for trends because of created and visually inspected for trends. To determine the uncertainty of trend analysis on short periods (less if the observed trends resulted from a chance arrange than 30 years) of streamflow records. ment of the data rather than from an actual change in streamflow, a statistical test (Mann-Kendall test) was Trend Detection Methods performed. The underlying test is for correlation between two variables (streamflow and time). The The approach to assess trends was based on an correlation coefficient Kendalfs tau was used to approach used by Lins and Slack (1999) to assess measure the strength of association between stream national streamflow trends. Although the statistical flow and time. The Mann-Kendall test is a nonpara methods are similar, the national study evaluated trends metric trend test (Helsel and lllisch, 1992) and uses a in streamflow in climate-sensitive streams with rank-based procedure that tests for one-directional drainage basins with limited anthropogenic (human (monotonic) changes over time. The test examines caused) influences. Streamflow trends in the Quin whether streamflow is increasing or decreasing mono nipiac River could be caused by flow diversions, tonically with time. wastewater discharges, flow regulation by dams and reservoirs, ground-water pumping, basin transfers, Three statistical parameters-Kendall's tau, p changes in land use and population, and climatic vari value, and Sen slope--are used to summarize the ability. results of the trend analysis. Kendall's tau ranges from -1 to + 1 and measures the strength of the trend. The Because of the large differences in streamflow strength of the trend increases as the value approaches characteristics between months and seasons, stream its upper or lower limits; values less than 0 indicate an flow data were subdivided into 14 indices to represent upward trend, and values greater than 0 indicate a different streamflow distributions. Streamflow from down ward trend. If there is no correlation between the same indices are compared and evaluated for trends streamflow and time, Kendall's tau equals 0. over time. The indices are based on a range of percen tiles from high to low flows. The range of percentiles The second statistical parameter used to summa evaluated for trends includes the annual maximum rize the trend results is the p-value. The p-value (lOoth_ ), 901h-, goth_, 701h-, 601h-, annual median measures the attained significance level of the statis csoth_ ), 40th-, 30th-, 2oth_, loth_, sth_, 2nd_, 1st_, and tical test (correlation) and is defined as the probability annual minimum (01h-) percentiles. The annual that a detected trend could have arisen by chance rather maximum and minimum percentiles represent the than from an actual change in streamflow. The p-value highest daily mean and lowest daily mean streamflow does not indicate the size or importance of a trend (for in a water year, respectively. example, magnitude of the streamflow trend); rather, it indicates whether the Kendall's tau value has any Different time periods were evaluated to provide significance. For this study, a p-value of 0.05 was information on how characteristics of streamflow selected as the critical attained significance level of the trends are affected by the length of record and to test. Where the p-value is less than or equal to 0.05, provide insight into regulation and natural variation of there is a less than or equal to 5-percent chance that the streamflow. Trend analyses were performed on time indicated significant trend actually is due to chance periods that were not heavily affected by droughts, rather than from an actual change in streamflow, and which may bias the trend results. Trend tests were the trend is than considered 95-percent reliable or performed for 30-, 40-, 50-, 55-, 60-, 65- to 70-year "believable." The p-value can be statistically signifi periods, all ending in water year 2000, except for two cant and the trend inconsequential at the same time. Streamflow Trend Analysis at the Wallingford Gaging Station 17 Drought Drought 0z 0 / (.) I ~ w J" (J) 1\ I \ 1\ r a: II ' I I I I I I I" w I \ I ', I; I 0.. I I I I I I \I J II tu 1,000 I w \/ I I u. I v (.) ii5 ::I (.) z 3" 0 ..Ju. :E 100 <( ~ ~ w II ' 1\ I I a: /''I 1I • / I II ,... ~ I \I I I ' .... ~ 1 I 1 I '-, ; 4 I ,... ' I 1 ; \ 1 I I ' (J) 1 \I 1 11 /"• I I 1 \ " I 1 I1 1"' ',J 1 I \ 1 V 1 I 1 J ~ 1 ( II \ ;'' I I I I \ I I I 1 1 I \ 1 1 1 1 I I I ~"' ~~ V ~ -1 I I I Y I I v"" I I 1 1 ,,! I I I I { / 1 • I/ II I I I If I"'\ I II If _, I 1/ f I 10 / 1930 1940 1950 1960 1970 1980 1990 2000 WATER YEAR EXPLANATION Ann ual maximum flow ---- Annual mean flow Annual median flow Annual minimum flow Figure 8. Annual maximum, mean, median, and minimum streamflow, Ouinnipi ac Rive r at Wallingford, Conn . (01196500), 1931-2000. Shaded areas represent statewide , multi-year droughts. To ill ustrate central patterns in st rea mflow data se nt the trend magnitude. The actu al trend magnitude as a function of time, a smooth lin e is added to the scat may differ significantly from the trend mag nitude esti l rplot of streamflow fo r the range of percentiles mated from the Sen slope; parti cul arl y where anomal ies analyzed fo r trend s. The smoothing procedure used is are near the beginning or the end of th e peri od of record LO WESS , locally we ight ed scatterpl ot smoothing (Lin s and Sl ack, 1999). The procedure for computing ( leveland , 1979). The smooth line is deri ved by the the Sen slope is described by Smith and others (1982). pattern of the data and indicates trend direc ti ons over Trend analyses we re performed on records of the rime. A smoothing factor is used to co ntrol the fit of prec ipitation and wastewater di scharge to eva luate th urve to the data and ranges from 0 to 1. Smaller whether these factors affected trends in strea mfl ow. mooth ing factors result in less smoothing of the curve The Mann -Kend all tes t was app lied to monthl y precip to th e data. A smoothing factor of 0.5 was used fo r the itati on and wastewater discharge record s to determine fi nal fit. the presence or absence of a trend in indi vidu al mo nths The Seasonal Kend all Slope Estimator (Sen and seasons. A variati on of the Mann -Kendall test, lope) is used to es ti mate the magnitude of the trend . know n as the seasonal Kendall test, was used to test fo r The Sen lope for strea mflow is ex pressed as a change overall trends. The seasonal Kend all test stati stic is in trea mflow per year, in cubic fe t per s con d. determ ined by calcul ati ng the Mann-Kendall test Alth ough the relation between strea mflow and time statis ti c for each month or season and combining the usuall y is non linea r, a linea r fu nction is used to repre- in divid ual test stati sti cs into a sin gle test statistic. The 18 Streamflow in the Qulnnlpiac River Basin, Connecticut- Statistics and Trends, 1931-2000 single test statistic represents the overall trend. Where detected in only the upper half of the flow distribution. seasons consistently show the same trend pattern, trend No decreasing flow trends were detected in any time results can be more significant by combining the indi periods or percentiles. Another important characteristic vidual test statistics into one overall test statistic. The is that most trends represent only modest increases in Mann-Kendall test statistic can incorporate an upward streamflow. trend in one season and a downward trend in another season that cancel each other, resulting in a seasonal The most statistically significant trend detected Kendall test statistic that indicates no overall trend. (highest Kendall's tau value and lowest p-value) is an upward trend in the annual minimum (daily mean) streamflow at the Wallingford gaging station. The Trends in Streamflow annual minimum streamflow coth percentile) increased by an average of 0.44 ft3 Is per year from 1931 to 2000 Trend test results, by percentile and by period of record, are summarized in table 5. Complete trend (fig. 9) . A LOWESS smooth line also shows an upward analysis results for streamflow are shown in appendix trend in the annual minimum flow since 1931 (fig. 9). l . Many similarities in trends are found across time The smooth line begins at its lowest point during the periods, across percentiles, and with respect to direc 70-year period, which coincides with the lowest tion. Increasing streamflows were detected predomi streamflow on record for the Quinnipiac River, then nantly in the lower half of the flow distribution (annual rapidly rises from 1931 until the early 1950's. From the minimum to annual median) and the extreme upper half early 1950's to 2000, the smooth line, which illustrates of the flow distribution (annual maximum flow), the relation between streamflow and time, continues to except during 1961-00, when upward trends were rise at a more gradual rate. Table 5. Trends for selected percentiles of streamflow between the annual minimum and annual maximum streamflows, Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000 [Kendall's tau values range from ·I to I; values less than 0 indicate an upward ttend, and values greater than 0 indicate a downward !rend; ; p-value. attained significance level of the !rend test; p-values in bold and shaded lines arc at the attained significance level of less than or equal to 0.05; median is the median value for the percentile; Sen slope is the change in stteamflow per year, in cubic feet per second;<, less than] Percentile Kendall's tau p-value Median Sen slope 1931-2000 (drought 1929-32) 0 percentile 0.357 <0.001 40.0 0.436 (annual minimum daily mean) I st percentile .281 <.001 46.3 .331 2nd percentile .253 .002 50.2 .313 5lh percentile .201 .014 55.9 .263 lOth percentile .171 .037 65.0 .235 20th percentile .151 .066 82.8 .250 30th percentile .153 .062 102 .358 40lh percentile .145 .077 125 .444 50th percentile (median) .151 .066 !56 .533 lOOlh percentile .253 .002 1.780 16.8 (annual maximum daily mean) 1935-2000 0 percentile .280 <.001 41.0 .333 (annual minimum daily mean) I st percentile .194 .021 46.8 .201 2nd percentile .176 .037 50.9 .204 !OOlh percentile .215 .on 1,860 15.7 (annual maximum daily mean) Streamflow Trend Analysis at the Wallingford Gaging Station 19 Table 5. Trends for selected percentiles of streamflow between the annual minimum and annual maximum streamflows, Ouinnipiac River at Wallingford, Conn. (01196500), 1931-2000-Continued [Kendall's tau values range from · I to I; values less than 0 indicate an upward trend, and values greater than 0 indicate a downward trend; ; p-value, attained significance level of the trend test; p-values in bold and shaded lines are at the anained significance level of less than or equal to 0.05 ; median is the median value for the percentile; Sen slope is the change in streamflow per year, in cubic feet per second;<, less than) Percentile Kendall's tau p-value Median Sen slope 1941-2000(drought1940-45) 0 percentile 0.167 0.060 43 .0 0.202 (annual minimum daily mean) 5th percentile .159 .073 57.2 .250 lOth percentile .193 .030 65.0 .314 20th percentile .200 .024 81.9 .391 30th percentile .214 .016 100 .530 40th percentile .189 .034 123 .650 50th percentile (median) .179 .044 158 .772 90th percentile .156 .078 418 1.84 IOOth percentile .241 .007 1,860 18.5 (annual maximum daily mean) 1945-2000 30th percenti 1e .158 .086 105 .441 lOOth percentile 0.247 0.007 1,980 20.8 (annual maximum daily mean) 1951-2000 I st percentile .179 .068 48.3 .233 2°d percentile .181 .064 52.2 .272 5th percentile .162 .099 59.1 .289 30th percentile .166 .091 105 .512 I ooth percentile .168 .086 2,100 16.8 (annual maximum daily mean) 1961-2000(drought 1961-69) 30th percentile .222 .045 109 .912 40th percentile .203 .067 132 1.18 50th percentile (median) .219 .048 160 1.53 60th percentile .227 .040 194 1.71 70th percentile .212 .056 232 1.85 goth percentile .221 .046 285 2.53 90th percentile .245 .027 414 4.42 1971-2000 No trends detected 20 Streamflow In the Qulnnlplac River Basin, Connecticut-Statistics and Trends, 1931-2000 Although the annual minimum flow trend was streamflow were detected during the 60- and 70-year the most statistically significant trend, it was not as periods. The increasing streamflow trend was detected significant in the shorter time periods. The annual at the 90th percentile (high flow) but not the 1001h Injnimum streamflow increased by an average of 0.44 percentile during the 40-year period; the trend was ft Is per year from 1931 to 2000 (p-value less than nearly significant (p-value = 0.086) during the 50-year 0.001 and Kendall's tau of0.357) as compared to 0.20 period. No trends were detected in the annual ft 3/s per year from 1941-00 (p-value of 0.060 and maximum streamflow during 1971-00. Land-cover Kendall's tau of0.167). Exceptionally low streamflows changes from pervious to impervious surface, expan were recorded through the 1930's that largely affect the magnitude of the annual minimum streamflow trend. sion of the storm-drainage systems, and increases in The unusually low flows of the 1930's are an anomaly rainfall intensity probably result in increases in annual for the period of record. After the drought of July 1929 maximum streamflow. to December 1932 (recurrence interval of more than Statistically significant uRward trends in the 25 years), the annual minimum streamflow remained annual median streamflow (501 percentile) were exceptionally low through 1938. The low streamflows detected during 1941-00 and 1961-00. The upward during that time period probably are caused by the extensive flow regulation. No trends were detected in trend in the annual median streamflow nearly was the annual minimum streamflow for the 30- or 40-year significant (p-value =0.066) during 1931-00. No periods ( 1961-00 and 1971-00) at the Wallingford trends were detected in the annual median streamflow gaging station. in the non-drought beginning time periods ( 1935-00, 1945--00, 1951-00 and 1971-00). Severe droughts at The second most statistically significant trend the beginning of the time period analyzed probably can detected is an upward trend in the annual maximum result in the detection of an increase in streamflow. The streamflow (fig. 10). Upward trends also were detected in the annual median streamflow (fig. 11). The annual LOWESS smooth line of the annual median stream maximum (1001h percentile) streamflow increased by flow pattern begins at its lowest point, which coincides an average of 16.8 ft3/s per year, and annual median with the 1930's drought, then gradually rises until the (50th percentile) streamflow increased by an average of early 1950's and dips during the 1960's drought (fig. 0.53 ft3 /s per year during 1931-00. Statistically signif 11 ). The smooth line rises from 1960 to 1980, then icant upward trends in the annual maximum daily mean gradually falls from approximately 1982 until 2000. 0 100rT--~--.---~-.--~--~--~~--~--~--~~--~---- z Annual mimmum flow= 0.44 • {water year- 1965.5) + 40 LOWESS smooth - 0 0 [approximate increase of 0.4 cubic feet per second per year) Sen slope w en p-value = 0.00001 a: Kendall's tau = 0.35 ~ 80 t w LL. 0 iD::> 60 0 ... ~ ... --·--· ...... -- ~ .. ---- 0 ...J ---- LL. 40 -< ::!: c:s: ----.. -----...... w --~· ....a: en --- ~ 20 ::> z~ ~ 0 1930 1940 1950 1960 1970 1980 1990 2000 WATER YEAR Figure 9. Trends in annual minimum streamflow, Quinnipiac River at Wallingford, Conn. (01196500), 1931-2000. Streamflow Trend Analysis at the Wallingford Gaging Station 21 0z 0 u 8,000,-,,------,------,----.------,------,-----,---, w Ill Annual maximum flow= 16.7 ·rwaler year -1965.5) + 1775 LOWESS smooth - a: [approximate increase of 17 cubic feet per second per year) • Sen slope ~ 7,000 p-value = 0.002 Iiiw Kendall's tau= 0.25 u.. u 6,000 - iii ::::l u 5,000 ~ :i 0 ii 4,000 - ::E ~ w a: 3,000 - !;; ::E ~ 2,000 - x ~ ::E .. ..J 1,000 - ~ ::::lz ~ 0 ~------~------L------~------L------~------L------~~ 1930 1940 1950 1960 1970 1980 1990 2000 WATER YEAR Figure 10. Trends in annual maximum stream fl ow, Ouinnipiac River at Wallingford, Conn. (01196500), 1931-2000. 300 z0 Annual median flow= 0.53 · [water yea r . 1965.5) + 156.25 LOWESS smooth-- 0 [a pproximate increase of 0.5 cubic teet per second per year) Sen slope u w p-value = 0.06 Ill 250 Kenda ll's tau = 0.15 a: w a. Iii w u.. 200 u _....._ iii __ ::::l u ---.. 150 ~ ~- 0 . . ..Ju.. .. ::E 100 w~ a: 1- Ill ::E 50 ::::l ::Ez ~ 0 1930 1940 1950 1960 1970 1980 1990 2000 WATER YEAR Figure 11. Trends in annual median streamflow, Quinnipiac River at Wallingford, Conn . (01196500), 1931 - 2000. 22 Streamflow in the Quinnipiac River Basin, ConnE!ctlcut-Statistics and Trends, 1931-2000 The highest number of statistically significant nings). Trends may be possible at significance levels trends (p-value <= 0.05) over all the percentiles is seen greater than 0.05. during the 60- and 70-year periods (1941-DO and The trend-analysis results only reflect stream 1931-00). A high number of trends also is evident flow patterns detected at the Wallingford streamflow during the 40-year period (1961-00) and 50-year gaging station. The station is approximately 14 mi from period (1951-DO). No statistically significant trends Long Island Sound and receives runoff and ground were detected during the most recent 30-year period water from 70 percent of the basin. The accuracy of (1971-00). For the 60- and 70-year periods (1941-DO transferring flow characteristics or trend results and 1931-DO), trends are detected in the low to middle upstream or downstream from the station was not eval range coth to percentile) and the uppermost percen soth uated for this study. Diversions, return flows, other tile (lOOth percentile). The trend pattern changes from regulation and natural changes in streamflow need to the lower half to the upper half of the streamflow be interpreted before flow characteristics can be trans percentile distribution during the most recent 40-year ferred to another location on the river. period (1961-00). Statistically significant trends (p-value <= 0.05 and Kendalrs tau value> 0.2) are detected in the middle to upper percentile range (30th to Factors That Affect Trends in Streamflow 9oth percentile) during 1961-DO. No statistically signif icant trends were detected in the 6oth to 90th percentiles Factors that may affect streamflow trends include (1) climatic variability, such as precipitation, for the periods analyzed, except during 1961-DO. and (2) human influences, such as wastewater Trend-analysis results are sensitive to the discharges, streamflow diversions, interbasins trans extreme climatic anomalies near the beginning and the fers, consumptive uses, and land-cover changes, such end of the record. Statewide droughts, from July 1929 as urbanization. Generally, streamflow diversions, out to December 1932, from September 1940 to April of-basin transfers, and consumptive uses decrease low 1945, and from August 1961 to November 1971 streamflow. Urbanization may cause an increase in (Weiss, 1991), can affect the trend-analysis results for runoff and flooding and a decrease in low streamflow. the 70-, 60-, and 40-year periods (1931-DO, 1941-DO, Relations between streamflow trends and trends in and 1961-DO). Because the results are sensitive to precipitation and municipal wastewater discharges extreme climatic anomalies early or late in the analysis were examined to determine the effects of precipitation period, a second series of trend analyses were and wastewater discharge on streamflow. Analyses of performed on non-drought beginning periods: 1935- the effects of human influences other than wastewater 00, 1945-00, 1951-DO, and 1971-DO. discharges are not included in this study. Fewer increasing streamflow trends were detected across the non-drought beginning time periods Precipitation than in the drought beginning time periods. Also, the Precipitation data were analyzed to evaluate magnitude of the trends was much lower and the whether streamflow trends on the Quinnipiac River attained significance of the statistical test was higher might be related to precipitation. Regional precipita for the non-drought beginning periods. For example, tion data were retrieved from the National Oceanic and the magnitude of the trend at the 30th percentile is Atmospheric Administration (NOAA), National higher and the attained significance of the trend test is Climatic Data Center database for the period 1930-00 more significant for the time periods beginning in a (data accessed on November 26, 2001 on the World drought (1941-DO-Kendall's tau of0.214 and p-value Wide Web at URL http://lwf.ncdc.noaa.gov/oal equal to 0.016; 1961-00-Kendall's tau of 0.222 and climate/climatedata.html). A precipitation dataset, both p-value equal to 0.045) than the time period not begin spatial and temporal, was compiled from five rain ning in a drought (1951-DO-Kendall's tau of 0.166 gages in south-central Connecticut (fig. 1; appendix 2). and p-value = 0.091). A number of trends were Four different precipitation indices were evaluated for detected with an attained significance level slightly trends: monthly total, annual total, annual median, and greater than 0.05 (0.06 to 0.1) in the lower half and annual mean. Monthly precipitation data from five rain extreme upper range of the flow distribution, and gages were averaged within each year to produce across time periods (droughts and non-drought begin- annual mean and annual median values, and summed Streamflow Trend Analysis at the Wallingford Gaging Station 23 each year to produce annual totals. When monthly data gages (NOAA station numbers 65077 and 64767) with for one or more of the five rain gages were missing, the nearly complete record. These two rain gages used to monthly average was based on the number of rain analyze monthly precipitation trends are missing less gages with data. A time-series plot of total annual than 1 percent of the rainfall data for the time period precipitation as the arithmetic average of the five rain analyzed. A Kendall tau test was performed to detect gages is shown in figure 12. Monthly precipitation trends in precipitation. totals were compiled by averaging data from two rain 80 LOWESS smooth CJ) 70 w J: (.) ~ 60 z~ 0 i= ~ 50 t- :.- - __. 0:: - (3 - w a: a. 40 ...J 10 1930 1940 1950 1960 1970 1980 1990 2000 CALENDAR YEAR Figure 12. Annual total precipitation for five rain gages in and near the Ouinnipiac River Basin, Conn., and LOWESS smooth line, 1930-2000. 24 Streamflow In the Qulnnipiac River Basin, Connecticut-Statistics and Trends, 1931-2000 The trend-analysis results on precipitation indi flow of2.1 Mgal/d (3.2 ft3/s) and were not included in cated that no significant trends are present at the 95- the trend analysis. percent significance level (p-value <= 0.05). The monthly precipitation total, annual precipitation total, To further understand the trend in annual and annual average (median and mean) precipitation minimum streamflow, the annual minimum streamflow totals show no statistical evidence of upward or down was plotted for the Southington and Wallingford ward trends during 1930-00. From this analysis, no stations for coincident time periods (fig. 13). (The evidence is available to indicate that precipitation may Southington station is upstream from the three munic be causing the increase in the annual minimum flow at ipal wastewater-treatment facilities.) Streamflow at the the Wallingford gaging station. Southington station is regulated by 15 industrial and A national research study on precipitation trends public-water diversions with a combined maximum indicates that extreme precipitation events, such as the daily withdrawal of 13.2 Mgalld, and 4 permitted 1-day rainfall intensity for coastal areas, are increasing surface-water discharges with a combined maximum (Karl and Knight, 1998). The magnitude of the daily flow of 0.732 Mgalld (Quinnipiac River Water maximum streamflow is a function of rainfall intensity. shed Partnership, 2000). The Southington station An increase in rainfall intensity as indicated in the would be expected to yield higher natural flows during national study of extreme precipitation events lends low-flow conditions than the Wallingford station support to an upward trend detected in the annual because the percentage of coarse-grained deposits (as maximum streamflow from 1931 to 2000. percent of total drainage area) is higher at Southington than at Wallingford. A comparison of annual minimum Wastewater Discharges streamflow at the two stations since 1988 shows that Wastewater discharges can augment streamflow. for the annual minimum streamflow, the yield per Of the 19 permitted wastewater discharges in the basin, square mile of basin generally is lower at Southington 12 are· upstream from the Wallingford gaging station than at Wallingford. Wastewater discharge may be with a combined maximum flow of 25 Mgal!d increasing the annual minimum streamflow at the Wall (38.7 fr3/s). Three of the 12 permitted discharges are ingford station, and diversions may be reducing the municipal wastewater-treatment facilities in Meriden, annual minimum flow at Southington. Cheshire, and Southington. Collectively, these three municipal wastewater-treatment facilities account for Wastewater records were obtained from each 92 percent of the permitted discharges (upstream from town's Water Pollution Control Department. Records the Wallingford gaging station) into the Quinnipiac were available in electronic form from 1985 to 2001 River with a combined maximum daily flow of ( 17 years) for Meriden and Cheshire and from 1983 to 3 22.9 Mgal/d (35.5 ft /s) and an average daily flow of 2001 (19 years) for Southington. Monthly total 3 15.8 Mgal!d (24.5 ft /s). The combined wastewater discharge data were available from the Meriden and discharges above the Wallingford streamflow-gaging Southington facilities; daily average discharge was station represent about 33 percent of the monthly available for the Cheshire facility. A boxplot of waste median streamflow in August at the station. Data from water discharge from the Meriden wastewater-treat the three municipal wastewater-treatment facilities ment facility shows monthly and seasonal variability in were analyzed for trends because of the large percentage of streamflow that these permitted the wastewater discharge data (fig. 14). A Kendall tau discharges represent. The other nine permitted waste statistical analysis was used to detect statistically water discharges (upstream from the Wallingford significant trends in monthly wastewater discharges. A gaging station) that make up the remaining 8 percent of p-value less than or equal to 0.05 was selected to indi permitted discharges have a combined maximum daily cate the presence of a statistically significant trend. Streamflow Trend Analysis at the Wallingford Gaging Station 25 c Wallingford z Southington 0 (.) w II) a: 0.6 w a.w 1-..J ~~ u.w ~~ ' Cll:J . ;::) 0 0.4 . Ucn . .... I ~a: ·.... ;... . ~w ;:a. Southington •• : 0 •,. . ..J . u. I I. :E ·...... 0.0 '---..L.--~-...L--...... 1....-...... 1...-.....L..-...... L---1.----IL.---"----...1.--...L--.....J....-.....1 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 WATER YEAR Figure 13. Annual minimum streamflow at two U.S. Geological Survey streamflow-gaging stations (Quinnipiac River at Wallingford, Conn.-01196500 and Quinnipiac River at Southington, Conn.-01195400), 1988-2000. [Wallingford station has 39 percent coarse-grained deposits, and Southington has 51 percent coarse-grained deposits.] 700 90th percentile 75th percentile 600 ...,_J: Median -z 25th percentile wo ~ 1Oth percentile ~:E <(CX: 500 J:W ()C. en en cz 400 a:O ..,_...Jw...J <(<( 3:~ 300 ._awz en- 100 0 JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC Figure 14. Monthly total permitted wastewater discharges into the Quinnipiac River from the wastewater-treatment facility in Meriden, Conn., 1985-2001. 26 Streamflow in the Quinniplac River Basin, Connecticut-Statistics and Trends, 1931-2000 Selected trends in wastewater discharges are between 1980 (115,785) and 2000 (126,515), and by summarized in table 6. Complete trend-analysis results 148 percent between 1930 (50,981) and 2000 for wastewater discharge are shown in appendix 3. (126,515) (data accessed on April19, 2002, on the Upward trends were detected at all three municipal World Wide Web at URLs wastewater-treatment facilities (fig. 15). The overall http://www.sots. state.ct.us/RegisterManual/ upward trends were 2.23 Mgal/month/year (about Section VII/Population 1900.htm and 2 ft3/s) at Meriden; 1.18 Mgal/monthlyear (about http://www.sots. state.ct. us/RegisterManual/ 1.2 ft3/s) at Southington; and an average 0.04 Mgal/d/year (about 1 ft3/s) at Cheshire. Trend-analysis Section VIIJPopulation 1970.htm). Population increases results by month for Meriden showed statistically in urban and suburban areas generally cause increases significant trends in February and March. No trends in water use, water consumption, and wastewater. In were detected in summer or early fall during low-flow recent years, many water-conservation practices (such conditions. Trend-analysis results by month for as modem plumbing fixtures and educational programs Cheshire showed statistically significant trends in all related to conservation) were implemented to reduce months except December and August. Trend-analysis the volume of wastewater generated~ however, the results for Southington showed statistically significant wastewater data (fig. 15) and trend-analysis results trends in January, February, and March. indicate that wastewater discharge increased from 1985 The population of the Meriden, Cheshire, and to 2000. A trend analysis of water use and consumption Southington has increased by about 9.3 percent was beyond the scope of this study. Tabte 6. Trends in permitted wastewater discharges at selected wastewater-treatment facilities, Quinnipiac River Basin, Conn. [Kendall's tau values range from -I to I; values less than 0 indicate an upward trend, and values greater than 0 indicate a downward trend; p-value, attained significance level of the trend test; p-values in bold and shaded lines are at the attained significance level of less than or equal to 0.05; median is the median value for the percentile; Sen slope is the change in wastewater discharge per year;<, less than] Trend Kendall's tau P-value Median Sen slope Meriden wastewater-treatment facility (1985-Ul; units are total million gallons per month) Overall trend (seasonal Kendall) 0.178 0.040 264 2.23 February .456 .012 294 6.86 March .529 .003 370 11.7 Cheshire wastewater-treatment facility (1985-01; units are average million gallons per day) Overall trend (seasonal Kendall) .477 <.001 1.93 .046 January .684 <.001 2.18 .065 February .691 <.001 1.99 .075 March .603 <.001 2.15 .080 April .485 .007 2.23 .086 May .441 .015 1.99 .054 June .463 .010 1.85 .055 July .485 .007 1.65 .038 August .353 .052 1.72 .027 .September .463 .010 1.77 .031 October .382 .036 1.84 .035 November .375 .039 1.91 .030 Southington wastewater-treatment facility (1983-01; units are total million gallons per month) Overall trend (seasonal Kendall) .205 <.001 117 1.18 January .368 .030 124 2.73 February .380 .025 113 1.76 March .555 .001 141 2.99 Streamflow Trend Analysis at the Wallingford Gaging Station 27 700 r------~ Regression line Y= 0.007x + 56.4 600 u.i .. (!) 500 4 a::tJ) .. :I:o~z ()..J " '&.. 4 ~..J 400 • • 4 • • • .... • ..... 4 • • ".. c~ • • • • • >0 .... • • 4 .... J.tt " ..Jz 300 " ..... 4...... \ .... ".. " i=2 .. .. + .... " 4 • • 4r Z..J 0::::! :E:E 200 ..JZ ....~ ....0 100 0 ,..... ,...... " Figure 15. Trends in wastewater discharges to the Quinnipiac River from the wastewater-treatment facility in Meriden, Conn., 1985-2001. From the wastewater-discharge trend analysis, An increase in the quantity of wastewater evidence indicates that wastewater discharge may be discharge may not necessarily cause an increase in increasing streamflow at the Wallingford gaging downstream flow, particularly on a regulated river or station. Both the LOWESS line of the annual minimum where the distance between the release point and study streamflows and Sen slope of annual minimum stream point is considerable (miles). Other factors affecting flows are consistent with an increase in wastewater low flow, such as water withdrawals and land-use discharges. The combined daily average wastewater changes, were not evaluated and cannot confirm or refute the possibility that increases in the annual discharge from the three facilities increased by about 4 minimum streamflow primarily are related to the ft 3/s (2.5 Mgalld) during 1985-01. Because the Sen increases in wastewater discharges. The storage slope from 1931 to 2000 is affected by the unusually capacity of the channel reach between the wastewater low flows in the 1930's, the Sen slope from 1941 to treatment facilities and the gaging station, particularly 2000 is used to interpret the relation between trends in the Community Lake reach, has not been analyzed and wastewater discharge and the annual minimum stream can be an important factor in controlling low-stream flow. The LOWESS line shows an increase in the flow characteristics. Additional investigation on water annual minimum flow of about 2 ft3/s (1.3 Mgal/d) and withdrawals, land-use changes, and the storage the Sen slope (from 1941 to 2000) shows an increase in capacity of the channel reach would be necessary to the annual minimum flow of about 3 ft3/s (1.9 Mgalld) better understand the effects of wastewater discharges at the gaging station during 1985-00. on streamflow trends. 28 Streamflow in the Quinnlplac River Basin, Connecticut-Statistics and Trends, 1931-2000 SUMMARY downward trends were detected for any time periods or percentiles. Significant streamflow trends were common in the lower half of the flow distribution The Quinnipiac River is an important resource in ranging from the annual minimum to annual median south-central Connecticut. In response to water alloca (Olh to 50th percentile) for periods longer than 40 years. tion and streamflow concerns in the basin, the USGS, During 1961-00, streamflow trends were detected in in cooperation with the Connecticut DEP, began a the middle to upper half of the flow distribution (30th to study in 2000 to compute current streamflow statistics 90th percentile). and analyze historical streamflow data for trends to document long-term changes. Streamflow statistics for Records of precipitation and wastewater two continuous-record streamflow-gaging stations on discharges were analyzed to provide insight into the Quinnipiac River (Wallingford-0 1196500 and streamflow trends. Trend-analysis results of precipita Southington-01195490) were updated using standard tion from rain gages in and near the basin indicate no USGS methods and computer software to estimate trends in annual or monthly precipitation totals during statistics for flow duration, low-flow frequency, annual 1930-00. The trend-analysis results for precipitation average streamflow, and monthly average streamflow. could not directly lend support to an upward trend in The flow statistics were estimated from an analysis of the annual minimum streamflow. A national research the historical streamflow record. Because the stream study on precipitation trends indicate increases in the flow is affected by diversions, wastewater discharges, rainfall intensity for Connecticut in the 20th century. reservoirs, ground-water pumping, basin transfers, and Increases in rainfall intensity lends support to an changes in land use and population, the streamflow upward trend in the annual maximum streamflow. statistics reflect regulated flow and not the natural flow Increases in residential and commercial development of the river. and expansion of storm-drainage systems may be causes of an upward trend in the annual maximum Low-flow frequency estimates from station data streamflow. varied by 10 percent at Wallingford and by 30 percent at Southington from the low-flow frequency estimates Wastewater discharges can constitute a substan from a regression equation. The 7Q10 for Wallingford tial percentage of streamflow in August and September from the regression equation is 10-percent less than the during low-flow conditions and during periodic 7Q10 calculated from the station data, indicating that droughts. A trend analysis of wastewater discharges for regulation (release of wastewater discharges) may be municipal wastewater-treatment facilities in Meriden, increasing the flow at Wallingford. The 7Q10 for Cheshire, and Southington indicates an increase in Southington from the regression equation is 30-percent wastewater discharge at each municipal wastewater greater than the 7Ql0 value calculated from the station treatment facility during 1985-01. Results of the trend data, indicating that diversions may be reducing flow at analyses provide evidence that wastewater discharge is Southington. increasing at a rate consistent with the annual minimum streamflow trend. Wastewater discharge increased by Streamflow trends were evaluated at the long about 4 ft3 Is and the annual minimum streamflow at the term gaging station in Wallingford using the non-para gaging station in Wallingford increased by approxi metric Mann-Kendall test. Trends were computed for a mately 2-3 ft3/s. range of percentiles of streamflow, from the annual minimum to annual maximum, and for a range of time Analyses of precipitation and wastewater periods, from 30 to 70 years. Trend results indicate that discharge provide general insight to what extent these the annual minimum and annual maximum streamflow trends have on the streamflow. Abnormally low flows increased by 0.44 ft3/s and 17 ft3/s per year, respec were recorded from 1932 to 1938 when annual precip tively, for the Wallingford gaging station during the itation totals were normal to above-normal. Graphical period of record (1931-00). The highest percentage of evidence suggests that regulation affected streamflow trends were detected in the 40-, 60- and 70-year periods in the early period of record (1930's). Conversely, the (1961-00, 1941-00 and 1931-00, respectively). recurrence of droughts in the early period (1930's, Increases in the annual maximum streamflow were 1940's and 1960's) and above-normal precipitation in conunon during all time periods, except during 1971- the 1970's indicates that the upward trends in stream 00, when no streamflow trends were detected. No flow (annual minimum to annual median) may, in part, SUMMARY 29 be a result of climatic variability. The magnitude of the Mazzaferro, D.L., Handman, E.H., and Thomas, M.P., 1979, trend in the annual minimum streamflow from 1931 to Water resources inventory of Connecticut, part 8, Quin 2000 at the Wallingford gaging station appears to nipiac River Basin: Connecticut Water Resources Bul letin 27, 88 p. reflect both regulation and periodic droughts in the Quinnipiac River Watershed Partnership, 2000, Preliminary early record. The extent that regulation and droughts assessment of water withdrawals and streamflows in affect the magnitude of the trends could not be deter the Quinnipiac River watershed: Hartford, Conn., mined readily and was outside the scope of the study. Quinnipiac River Watershed Partnership Work Group Wastewater discharges appear to be affecting some Report, July 2000, Hartford, Conn., 37 p. Ries, K.G., Ill, 2000, Methods for estimating low-flow sta streamflow trends. Increases in both the wastewater tistics for Massachusetts Streams: U.S. Geological Sur discharges and the annual minimum streamflow seem vey Water-Supply Paper 00-4135, p. 7-9. to indicate that the annual minimum streamflow at the Ritzi, Charles, and Associates, 1987, Computation of Wallingford gaging station has been augmented by USFWS aquatic base flow for regulated streams: Win upstream wastewater discharges. throp, Maine, 15 p. Searcy, J.K., 1959, Flow-duration curves, Manual of hydrol The streamflow statistics and trend-analysis ogy-Part 2, Low-flow techniques: U.S. Geological results presented here provide a limited understanding Survey Water-Supply Paper 1542-A, 33 p. and assessment of the water quantity in the Quinnipiac Smith, R.A., Hirsch, R.N., and Slack, J.R., 1982, A study of River; however, many uncertainties are associated with trends in total phosphorus at NASQAN stations: U.S. Geological Survey Water-Supply Paper 2190, 34 p. factors causing streamflow trends. A watershed-simu Thomas, M.P., 1966, Effect of glacial geology upon the time lation model could, for example, provide valuable distribution of streamflow in eastern and southern Con information about the effects of the withdrawals and necticut: U.S. Geological Survey Professional Paper discharges on streamflow. Both natural effects and 550-B, p. B209-B212. human influences that affect streamflow trends need U.S. Fish and Wildlife Service, 1981, Interim regional policy for New England streamflow recommendations: Con further investigation to understand the effects of regu cord, N.H.,U.S. Fish and Wildlife Service, Region 1, lation and climate on the Quinnipiac River. 3 p. Weiss, L.A., 1983, Evaluation and design of a streamflow REFERENCES CITED data network for Connecticut: Connecticut Water Resources Bulletin 36, 30 p. --1991, Connecticut floods and droughts, with a sec Cervione, M.A., Jr., 1982, A method for estimating the 7- tion on "water management" by C.J. Hughes, in Paul day, 10-year low flow of streams in Connecticut: Con son, R.W., Chase, E.B., Roberts, R.S., and Moody, necticut Water Resources Bulletin 34, p. 17 p. D.W. (compilers), National Water Summary 1988- Cleveland, W.S., 1979, Robust locally weighted regression 89-Hydrologic events and floods and droughts: U.S. Geological Survey Water-Supply Paper 2375, and smoothing scatterplots: Journal of American Statis p. 215-222. tical Association, v. 74, no. 368, p. 829-836. Connecticut Department of Environmental Protection, 1997, Connecticut water quality standards and criteria: Hart ford, Conn., Inland Water Resources Division, Con necticut Department of Environmental Protection, 46 p. Helsel, D.R., and Hirsch, R.M., 1992, Statistical methods in water resources: Studies in Environmental Science 49, New York, Elsevier Science Publishers, 529 p. Karl, T.R., and Knight, R.W., 1998, Secular trends of precip itation amount, frequency, and intensity in the USA: Bulletin of the American Meteorological Society, v. 79, p. 231-241. Lins, H.F., and Slack, J.R., 1999, Streamflow trends in the United States: Geophysical Research Letters, v. 26, no. 2, p. 227-230. 30 Streamflow in the Qulnnipiac River Basin, Connecticut-Statistics and Trends, 1931-2000 APPENDIXES Appendixes 31 Appendix 1. Trend results of selected percentiles of streamflow between the annual minimum and annual maximum , Quinnipiac River at Wallingford, Conn ., 1931-2000 [K endall's tau val ues range from -Ito I; val ues less than 0 indicate an upward trend, and values greater than 0 indicate a downward trend p-value, attained significance level of the trend test; p-values in bold and shaded lines are at the attained significance level of less than or equal to 0.05; median is the median value for the percentile; Sen slope is the change in streamflow per year, in cubic feet per second; <.less than] Percentile Kendall's tau p-value Median Sen slope 1931-2000 (drought 1929-32) 0 percentile 0.357 <0.001 40.0 0.436 (an nual minimum daily mean) I 51 percentile .281 <.001 46.3 .331 211d percentile .253 .002 50.2 .313 5th percentile .201 .014 55.9 .263 1 10 h percentile .171 .037 65 .0 .235 20th percentile .151 .066 82.8 .250 30th percentile .153 .062 102 .358 40th percentile .145 .077 125 .444 50th percentile (median) .151 .066 156 .533 60th percentile .127 .12 1 192 .518 70th percentile .093 .256 232 .467 80th percentile .098 .232 292 .583 90th percentile .133 .105 417 1.21 I 00111 percentile .253 .002 1,780 16.8 (annual maximum daily mean) 1935-2000 0 percentile .280 <.001 41.0 .333 (annual minimum daily mean) I 51 percentile .194 .021 46.8 .201 2nd percentile .176 .037 50.9 .204 5th percentile .136 .107 58.0 .200 1 10 h percentile .138 .104 65 .7 .200 1 20 h percentile .117 .165 84.3 .205 30th percentile .117 .168 103 .286 40th percentile .094 .268 129 .338 50th percentile (median) .092 .276 160 .333 60th percen til e .073 .388 195 .300 70th percentile .044 .607 236 .238 80th percentile .051 .550 299 .324 90th percentile .103 .223 419 1.02 I oolh percentile .215 .011 1,860 15.7 (annual maximum daily mean) Appendix 1 33 Appendix 1. Trend resu lts of selected percentiles of streamflow between the annual minimum and annual maximum, Quinnipiac River at Wallingford, Conn., 1931-2000-Continued [Kenda ll 's ta u values range fro m -I to I; va lues less than 0 indicate an up wa rd trend, and values greater than 0 indica te a downward trend p-va lue, attained signiftcancc level of the trend test: p- values in bo ld and shaded lines are at the attained significance level of less than or equal to 0.05 : medi an is the median va lue for the percent ile: Sen slope is the change in streamfl ow per yea r, in cubic feet per seco nd :<, less than ] Percentile Kendall's ta u p-va lue Median Sen slope 1941-2000(droughtl940-45) 0 percentile 0. 167 0.060 43.0 0.202 (annual minimum dai ly mean) l 51 percentile .145 .102 47.3 . 166 2nd percent ile .145 .104 51.3 . 199 5th percentil e . 159 .073 57.2 .250 LOth percentile .193 .030 65.0 .314 20th perce ntil e .200 .024 81.9 .39 1 1 30 h percentile .2 14 .016 100 .530 40th percentile .189 .034 123 .650 50th percentile (median) . 179 .044 158 .772 60th percentile .145 . 102 194 .7 16 701h percent ile .1 18 . 185 232 .709 s o'" percentile .124 .162 294 882 901h percentile . 156 .078 4 18 1 84 1ooth perce ntile .241 .007 1,860 18.5 (a nnual maximum daily mean) 1945-2000 0 percentile .125 .174 44.0 .167 (annual minimum daily mean) 151 percentil e .114 .216 48.3 .139 211 d percentile . 105 .258 52.2 .176 5111 percenti le .110 .235 59. 1 . 188 I 01h percentil e .136 .140 66.7 .262 20th perce ntil e . 142 .12 5 84 3 .323 30th pe rcentile 158 .086 105 .441 40th pe rcentile . 136 .140 128 .532 50th percentile (medi an) .133 .149 160 .619 6oth percentil e .083 .369 195 .368 70th percentile .045 .631 237 .273 goth percen tile .061 .5! I 298 .41 3 90th percentile . 107 .246 426 1.34 I ooth percentil e .247 .007 1,980 20.8 (annual max imum dai ly mean) 34 Streamfl ow in th e Qu lnnlplac River Basin, Connecticut-Statistics and Trends, 1931-2000 Appendix 1. Trend results of selected percentiles of streamflow between the annual minimum and annual maximum, Quinnipiac River at Wallingford, Conn., 1931 - 2000-Continued [Kendall"s tau valu es ran ge from -I to I; values less than 0 indicate an upward trend , and values greater than 0 indicate a downward trend p-va lue, attained significance level of the trend test; p-values in bold and shaded lines are at the attained significance level of less than or equal to 0.05 ; median is the median value for the percen tile; Sen slope is the change in streamflow per year, in cubic feet per second; <, less than] Percentile Kendall's tau p-value Median Sen slope 1951- 2000 0 percentile 0.158 0.106 44.0 0.227 (annual minimum daily mean) l 51 percentile .179 .068 48.3 .233 211d percentile .181 .064 52.2 .272 51h percenti le .1 62 .099 59.1 .289 I Oth percenti le .149 .130 66.7 .329 20th percentile .145 .139 84.3 .375 30111 percenti le .166 091 105 .5 12 40th percentile .130 . 186 128 .593 5oth percenti le (median) .122 .213 160 .670 60u1 percentile 087 .380 194 .524 70111 percenti le .044 .657 23 7 .321 80th percenti le .056 .569 298 .436 901h percenti le .091 .353 433 1.31 I00U 1 percentile .168 .086 2, 100 16.8 (annual maxim um dail y mean) 1961 - 2000 (drought 1961-69) 0 percenti le .176 .113 44.5 .306 (annual minimum dail y mean) I st percentile .144 .196 49.4 .278 2"d percenti le .1 2 1 .278 53.9 .256 slh percenti le .124 .263 60.5 .302 lOu' perce ntil e .142 .200 67.5 .444 20U1 percent il e .153 .169 85.8 .500 30tl' percentile .222 .045 109 .912 401h perce ntil e .203 .067 132 1.18 soil' percentile (median) .2 19 .048 160 1.53 601h percentile .227 .040 194 1.71 7oth percentile .212 .056 232 1.85 SOU' percenti le .22 1 .046 285 2.53 90th percenti le .245 .027 414 4.42 IOO U' percentil e .179 .105 2,180 22.7 (ann ual maxi mum daily mean) Appendix 1 35 Appendix 1. Trend results of selected percentiles of streamflow between the annual minimum and annual maximum, Ouinnipiac River at Wallingford, Conn ., 1931-2000-Continued [Kendall's tau values range from -I to I; va lues less than 0 indicate an upward trend, and values greater tban 0 indicate a downward trend p-value, attained significance level of the trend test; p-values in bold and shaded lines are at tbe attained significance level of less tban or equal to 0.05; median is the median value for the percentile; Sen slope is the change in streamflow per year, in cubic feet per second;<. less than) Percentile Kendall's tau p-value Median Sen slope 1971-20<)0 0 percentile 0039 0.775 48.0 0.111 (annual minimum daily mean) Is t percentile -.103 .432 52.1 -.272 2nd percentile -.140 .284 57.0 -.358 sth percentile -.133 .309 65 3 -.362 10th percentile -.133 .309 75.7 -.375 20th percentile -.138 .292 900 -.583 30th percentile -.506 .708 112 -.300 40th percentile -.074 .580 138 -.486 5oth percentile (median) -.078 .556 171 -.857 60th percent i Ie -.110 .402 205 -.862 70th percentile -.092 .486 248 -.777 80th percentile -.030 .830 312 -.800 90th percentile -.021 .887 452 -.545 IOoth percentile -.051 .708 2.380 -8 .18 (annual maximum daily mean) 1931-1960 0 percentile .566 <.001 33.5 1.29 (mmual minimum daily mean) 1st percentile .368 .005 42.0 .920 2nd percentile .278 .032 45.1 .760 5th percentile .184 .158 52.5 .385 Ioth percentile .076 .568 61.7 .118 20~' percentile .253 .858 81.0 <.001 30th percentile .064 .630 98 .5 .350 40th percent ile .097 .464 120 .667 50 111 percentile (median) .113 .392 148 1.07 60th percentile .154 .239 183 1.50 70~' percentile .166 .205 231 1.77 goth percentile .191 .144 298 2.24 90th percentile .182 .164 417 2.71 I OOth percentile .101 .443 1,490 12 .5 (annual maximum daily mean) 36 Streamflow In the Qulnnlpiac River Basin, Connecticut-Statistics and Trends, 1931-2000 Appendix 1. Trend results of selected percentiles of streamflow between the annual minimum and annual maximum, Quinnipiac River at Wallingford, Conn., 1931-2000-Continued (Kendall's tau values range from -1 to 1; values less than 0 indicate an upward trend, and values greater than 0 indicate a downward trend p-value, attained significance level of the trend test; p-values in bold and shaded lines are at the attained significance level of less than or equal to 0.05; median is the median value for the percentile; Sen slope is the change in streamflow per year, in cubic feet per second;<, less than] Percentile Kendall's tau p-value Median Sen slope 1941-1970 0 percentile -0.005 0.986 39.0 <0.001 (annual minimum daily mean) 1st percentile -.140 .284 42.8 -.263 2nd percentile -.129 .326 45.6 -.222 5th percentile -.087 .509 51.6 -.133 1oth percentile -.021 .886 60.7 -.077 20th percentile -.007 .972 75.9 <.001 30th percentile .009 .957 90.8 .087 40111 percentile -.021 .887 116 -.174 50th percentile (median) -.064 .630 133 -.364 6oth percentile -.090 .498 170 -.859 70th percentile -.094 .475 211 -.975 80th percentile -.076 .568 263 -1.36 90th percentile -.113 .392 366 -2.26 lOOth percentile -.030 .830 1,510 -1.67 (annual maximum daily mean) Appendix 1 37 Appendix 2. Trend results of annual and monthly precipitation data for selected stations in Connecticut, 1930-2000 [Regional precipitation data from National Oceanic and Atmospheric Administration (NOAA), National Climatic Data Center (data accessed on November 26, 2001 on the World Wide Web at URL http:l/lwf.ncdc.noaa.gov/oalclimate/climatedata.html). Kendall's tau values range from -1 to 1; values less than 0 indicate an upward trend, and values greater than 0 indicate a downward trend; p-value, attained significance level of the trend test; p-values in bold are at the attained significance level of less than or equal to 0.05; median is the median value for the percentile; Sen slope is the change in wastewater discharge per year; <, less than) Kendall's tau P-value Median Sen slope Annual precipitation (NOAA station numbers 65077,64767,67432, 69759, and 66597) Annual total 0.047 0.568 50.4 0.028 Annual median .024 .784 3.80 .001 Annual mean .031 .732 4.16 .002 Monthly total precipitation (NOAA station numbers 65077 and 64767) January -.048 .588 3.34 -.010 February -.021 .813 3.10 -.002 March -.036 .690 4.14 -.006 April -.025 .779 4.12 -.004 May -.045 .610 4.07 -.008 June -.088 .316 3.20 -.014 July .099 .262 3.85 .016 August .018 .837 3.48 .003 September .082 .350 3.56 .014 October .158 .073 3.38 .026 November -.020 .828 4.48 -.006 December -.039 .663 4.27 -.006 Appendix 2 39 Appendix 3. Trend results of wastewater-discharge data from municipal wastewater-treatment facilities in Meriden, Cheshire, and Southington, Conn., 1985-2001 [Kendall's tau values range from -I to I; values less than 0 indicate an upward trend, and values greater than 0 indicate a downward trend; p-value , attained significance level of the trend test; p-values in bold and shaded lines are at the attained significance level of less than or equal to 0.05; median is the median value for the percentile; Sen slope is the percent change of median wastewater discharge per year; <, less than] Trend Kendall's tau p-value Median Sen slope Meriden wastewater-treatment facility (1985-01; units are total million gallons per month) Overall trend (seasonal Kendall) 0.178 0.040 264 2.23 January .309 .091 318 6.53 February .456 .012 294 6.86 March .529 .003 370 11.7 April .191 .303 378 4.41 May .140 .458 278 2.60 June .265 .149 217 2.74 July .265 .149 207 1.48 August .044 .837 215 .612 September .118 .536 204 .775 October .044 .837 223 .303 November -.132 .484 245 -1.08 December -.088 .650 301 -3.20 Cheshire wastewater-treatment facility (1985-01; units are average million gallons per day) Overall trend (seasonal Kendall) .477 <.001 1.93 .046 January .684 <.001 2.18 .065 February .691 <.001 1.99 .075 March .603 <.001 2.15 .080 Apri.l .485 .007 2.23 .086 May .441 .015 1.99 .054 June .463 .010 1.85 .055 July .485 .007 1.65 .038 August .353 .052 1.72 .027 September .463 .010 1.77 .031 October .382 .036 1.84 .035 November .375 . .039 1.91 .030 December .294 .108 1.98 .029 Appendix 3 41 Appendix 3. Trend results of wastewater-discharge data from municipal wastewater-treatment facilities in Meriden, Cheshire, and Southington, Conn., 1985-2001-Continued I Kendall's tau values range fr om - I to I; values less than 0 indicate an up ward trend, and values greater than 0 indicate a downward trend; p-value. attained signif1 cance level of the trend tes t; p-values in bold and shaded lines are at th e attained significance level of less th an or equal to 0.05 ; median is the median value fo r the percentile; Sen slope is the percent change of median was tewater discharge per year; <, less than] Trend Kendall's tau p-value Median Sen slope Southington wastewater-treatment facility (198~1; units are total million gallons per month) Overall trend (seasonal Kendall ) 0.205 <0.001 ll7 1.18 January .368 .030 124 2.73 February .380 .025 113 1.76 March .555 .001 141 2.99 April .088 .624 152 .985 May .076 .674 131 .508 June .193 .263 116 1.33 Jul y .3 10 .069 11 3 1.17 August .228 .184 107 1.1 8 September .041 .834 104 .242 October .076 .675 105 .591 November .146 .401 104 .834 December -. 006 1.00 119 -.044 42 Streamflow in the Quinniplac River Basin, Connecticut-Statistics and Trends, 1931-2000 Ahearn, 2002-Streamflow in the Quinnipiac River Basin, Connecticut-Statistics and Trends, 1931-2000- U.S. Geological Survey WRIR Report 02-4217